Antagonists of histamine H.sub.2 -receptors are known to inhibit the stomach secretions of humans and animals. The known antagonists include guanidine derivatives, such as:
[N-cyano-N'-methyl-N"]-2(4-methyl-imidazolyl)-methylthio[ethylguanidine] ("cimetidine"), U.S. Pat. No. 3,950,353; and
ranitidine-[N-[2]-(5-dimethylaminomethyl-2-furanyl)-methyl]thioethyl-[N-met hyl-2-nitro-1,1-ethenediamine], Great Britain Pat. No. 1,565,966.
These antagonists are effective in suppressing histamine and pentagastrin stimulated secretions. There are, however, serious disadvantages and side effects related to their use. Cimetidine, for example, may cause or exacerbate erosion of the stomach-duodenal mucous membranes, stomach cancer, perforation, pancreatitis, bradicardia, leucopenia, agranulocitoma, dermic hypersensitivity, autoimmunic hemolytic hepatitis, hypereglycemia, and muscle pains. H. Kato et al, Arch. Pharmacol. et Therapie, 249(2), pp. 247-56 (1981).
Other known compounds include 4-phenyltetrahydroisoquinolines of the formula I: ##STR1## wherein R.sub.1, R.sub.3, and R.sub.4 are each a hydrogen, a lower alkyl, or an aralkyl group; R.sub.2 and R'.sub.2 are each a hydrogen, a halogen atom, a trifluormethyl group, an alkyl, alkoxy, or aralkoxy group; and R.sub.5 is a hydrogen or halogen atom, a hydroxylic, trifluormethyl, or nitro group, or a lower alkyl, alkoxy, or aralkoxy group. These compounds are antidepressants, a well-known species of which is 4-phenyl-2-methyl-8-amino-1,2,3,4-tetrahydroisoquinoline hydrogen maleate ("nomiphenzene"). Great Britain Pat. No. 1,670,694.
Another known compound is 2-metoxycarbonyl-4-(betapiperidinoethyl)benzophenone hydrochloride ("baralginketone"), which has a spasmolytic and analgesic effect. C.A. 50, 9623c, E. Lindner, Arzn. Forsch., 6, pp. 124-7 (1956).